Conservative dentistry and oral pathology suggest therapeutic treatment of a carious tooth rather than extraction thereof. Consequently, the endodontic treatment technique of root canal operations involving removal of the pulp, treatment of the canal and filling thereof, are being carried out with increasing frequency.
In performing a root canal operation, it is extremely important for the dentist to accurately determine the length of the root canal when removing pulp therefrom and inserting a filling material therein. For instance, if the dentist should fail to reach the apex of the root canal, healthy tissue may be injured or the decayed pulp is allowed to remain which eventually may result in periodontitis or endodontis.
Generally, the endodontic treatment comprises the steps of opening the carious cavity, cutting the enamel caries, removing the coronal pulp, enlarging the root canal orifice, exploring the root canal, extracting the radicular pulp, enlarging the root canal, and filling the root canal. Normally, numerous probe instruments will be employed to perform this treatment method, including cleansers, reamers, files, and filling tools. Heretofore, the most complex, time-consuming and difficult step in the root canal operation has involved determining the depth of penetration of a reamer or file and precisely controlling and limiting the depth of such reamer or file so as not to penetrate either beyond the root apex or short thereof. One previous method of measuring the root canal length involved the insertion of a thin, flexible probe or explorer into the canal and performing x-ray of the carious tooth in order to determine the depth of penetration of the probe into the canal. Once the accurate measurement had been taken, successively used tools could be set to the proper penetration depth determined by the dentist.
Various instruments have been devised in the past for measuring probe penetration in a root canal, as evidenced by the disclosures of U.S. Pats. Nos. 3,916,529; 3,993,044; 3,753,434; 3,894,532; 3,660,901; and, 3,901,216, however, none of the instruments disclosed by such patents has been completely satisfactory in indicating the position of the probe relative to the canal apex with a high degree of sensitivity and accuracy. In this respect, one of the principal of the problems associated with previous instruments relates to the fact that the meters used by such instruments for visually indicating the penetration depth of the probe includes too many graduations to clearly depict the critical point at which the probe actually reaches the canal apex but does not penetrate through such apex inadvertently. In order to overcome the above discussed deficiency, some prior art instruments have provided means for actuating an audible or visual alarm, such as a light, when the probe achieves penetration to a critical point immediately adjacent the apex of the root canal. This solution is unsatisfactory because the dentist is not provided with feedback regarding the rate at which the probe is approaching the apex of the canal and may result in the probe going beyond such apex in the event that the dentist's reaction time after actuation of the alarm is not sufficient to slow or discontinue insertion of the probe after the latter has reached a critical point adjacent the canal apex. Furthermore, the use of audible alarms is undesirable since sounds produced by such alarms may be difficult to distinguish in the case of high ambient background noise.